The invention relates to a reflector telescope including a tube disposed in a spherical casing wherein the spherical casing is mounted in an outer framework. Such a reflector telescope is known from U.S. Pat. No. 3,791,713. Therein, the spherical casing is supported within the outer framework on an air cushion, and is rotatable by means of special drives about the polar and declination axis. The expenditure for the two different driving systems, by means of which the spherical casing is rotatable independently about its two axes, is disadvantageous. It is disadvantageous, further, that access to the sphere itself is variable according to the position of said casing, thus complicating access to the observation cabins assigned to the tube.